Wedges with q-axis damper circuits

ABSTRACT

A rotor for an electrical machine includes a rotor core having a plurality of circumferentially spaced apart rotor poles. Windings are seated in gaps between circumferentially adjacent pairs of the rotor poles. A wedge secures the windings in each gap. The wedge includes a first member made of a first material and at least one second member made of a second material. The second material has a higher electrical conductivity than the first material. The wedge is configured to supply Q-axis damping. A pair of end plates is connected electrically to the at least one second member at opposing longitudinal ends thereof thereby completing a Q-axis winding circuit for each wedge.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/470,525 filed Mar. 27, 2017 now issued as U.S. Pat. No. 10,541,580 onJan. 21, 2020, which is incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to electrical machines, and moreparticularly to quadrature axis (Q-axis) damping in electrical machines.

2. Description of Related Art

One of the problems that face synchronous machines is the ability toreject disturbances caused by speed transients or load fluctuations andimbalances. In response to the electrical and mechanical disturbances,conventional synchronous machines have damper bars embedded into therotors. The typical practice is to embed the damper bars in the directaxis of salient pole generators. However, this leaves the Q-axisundamped because the windings occupy the space between the poles of therotor and it is typical to insert a wedge in the gap to hold thewindings in place.

For high speed applications of electrical machines such as motors andgenerators, Q-axis damper windings are not practical because the wedgethat holds the windings in place occupies the space where the Q-axisdamper winding would occupy. The wedges are typically made of Inconel ortitanium which is consistent in regards to poor conducting materials. Inlow speed applications, electrically conductive materials such asaluminum or copper can be used for the wedges. But these materials lackthe strength needed in high speed, and/or high temperature applications.Additionally, the conductive wedge materials used in conventional lowspeed applications are typically electrically connected using brazejoints, which are not strong enough for high speeds.

The conventional techniques have been considered satisfactory for theirintended purpose. However, there is an ever present need for improvedQ-axis damping. This disclosure provides a solution for this problem.

SUMMARY OF THE INVENTION

A rotor for an electrical machine includes a rotor core having aplurality of circumferentially spaced apart rotor poles. Windings areseated in gaps between circumferentially adjacent pairs of the rotorpoles. A wedge secures the windings in each gap. The wedge includes afirst member made of a first material and at least one second membermade of a second material. The second material has a higher electricalconductivity than the first material. The wedge is configured to supplyQ-axis damping. A pair of end plates is connected electrically to the atleast one second member at opposing longitudinal ends thereof therebycompleting a Q-axis winding circuit for each wedge. The first member andthe at least one second member can be configured with no clearance spacetherebetween

The first material can have a higher mechanical strength than that ofthe second material. The first material can have a higher melting orglass transition temperature than that of the second material. At leastone electrically conductive damper bar can extend along an outer portionof each of the rotor poles, wherein each damper bar is connectedelectrically to the end plates for D-axis damping. The second materialof the wedges and the damper bars provide the rotor with full 360°damping, circumferentially.

The second material in each wedge can form a wedge damper bar extendingaxially through the respective wedge. The at least one second member canbe a Q-axis damper bar extending axially through the respective firstmember The second material in each wedge can form a plurality of damperbars extending axially through the respective wedge. The at least onesecond member can be a plurality of second members extending axiallythrough the respective first member. The second material in each wedgecan form at least one damper bar extending axially through therespective wedge, wherein at least one damper bar has an axialcross-section with a perimeter shaped for optimizing skin effect. The atleast one second member can have an axial cross-section with a perimetershaped for optimizing skin effect, for example arc shaped. The at leastone second member can be intimately radially surrounded by the firstmember.

Each wedge can have two axially opposed end portions of a third materialwith more electrically conductive material than the first material forelectrical connection between the second member and the end plates,e.g., the third material can be the same material as the secondmaterial. Each wedge can be manufactured by combining the first andsecond materials, e.g., by additive manufacturing.

A method of manufacturing a rotor wedge on an electrical machineincludes additive manufacturing of a wedge body with layers that includea first material and a second material having a higher electricalconductivity forming a damper bar in the wedge body. Additivemanufacturing can combine dissimilar materials into each layer, such asusing a material with higher electrical conductivity than that of thefirst material on axially opposed end portions of the wedge body forelectrical connection of the damper bar with end plates of a rotor.

These and other features of the systems and methods of the subjectdisclosure will become more readily apparent to those skilled in the artfrom the following detailed description of the preferred embodimentstaken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosureappertains will readily understand how to make and use the devices andmethods of the subject disclosure without undue experimentation,preferred embodiments thereof will be described in detail herein belowwith reference to certain figures, wherein:

FIG. 1 is a schematic perspective view of an exemplary embodiment ofapportion of an electrical machine constructed in accordance with thepresent disclosure, showing the D-axis and the Q-axis on a rotor;

FIG. 2 is a schematic end elevation view of a portion of the rotor ofFIG. 1, showing the damper bar in the wedge; and

FIG. 3 is a schematic end elevation view of a portion of the rotor ofFIG. 1, showing another exemplary embodiment of a damper bar in thewedge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectdisclosure. For purposes of explanation and illustration, and notlimitation, a partial view of an exemplary embodiment of an electricalmachine in accordance with the disclosure is shown in FIG. 1 and isdesignated generally by reference character 100. Other embodiments ofelectrical machines in accordance with the disclosure, or aspectsthereof, are provided in FIGS. 2-3, as will be described. The systemsand methods described herein can be used to provide quadrature axis(Q-axis) damping in high speed rotors of electrical machines wheretraditional rotors either lack Q-axis damping, or have some Q-axisdamping structure that is too mechanically weak to support high speeds,e.g., 20,000 to 50,000 RPM.

A rotor 102 for the electrical machine 100 includes a rotor core 104having a plurality of circumferentially spaced apart rotor poles 106.Windings 108 are seated in gaps 110 between circumferentially adjacentpairs of the rotor poles 106. A respective wedge 112 secures thewindings 108 in each gap 110. The rotor 102 rotates about axis A underforces created by stator 114 in a motor, or in a generator, the rotor102 is driven by a prime mover. D-axis damper bars 116, only some ofwhich are labeled in FIG. 1 for sake of clarity, are provided in each ofthe poles 106 to provide damping for the D-axis in each pole 106, whereone of the D-axes is identified in FIG. 1, which is the axis for themain flux for driving rotor 106 about axis A. Additional damper bars,e.g., as second member 120 described below, are provided in thematerials of the wedges 112 to provide damping in the quadrature axis(Q-axis) through each gap 110, where one of the Q-axes is shown in FIG.1.

With reference now to FIG. 2, each wedge 112 includes a first member 118made of a first material, such as titanium or Inconel, and a secondmember 120 made of a second material, such as copper, beryllium copper,or aluminum, with a higher electrical conductivity than that of thefirst material forming a damper bar for Q-axis damping. A pair of endplates 122, one of which is shown in FIG. 1, is electrically connectedto the second member 120 of each of the wedges 110 to complete a Q-axiswinding circuit for each wedge 110.

The first member 118 has a higher mechanical strength than that of thesecond member 120, providing strength for high speed rotation and/orhigh temperature operation, and the high electrical conductivity of thesecond material provides the electrical circuit for the Q-axis damperwindings. It is also contemplated that the first material can have ahigher melting or glass transition temperature than that of the secondmaterial. With electrically conductive damper bars 116 extending alongan outer portion of each of the rotor poles 106, wherein each damper baris 116 electrically connected to the end plates 122 for D-axis damping,and with the second member 120 of the wedges 112, the collective damperbars 116/120 provide the rotor 102 with full 360° damping, where 360° isin reference to the direction wrapping circumferentially around rotationaxis A of FIG. 1.

The second member 120 in each wedge 112 forms a wedge damper barextending axially through the respective wedge 112 from end to end. Asshown in another embodiment shown in FIG. 3, the second member 120 ineach wedge 112 can form a plurality of damper bars 220 each forming anarc-shaped cross-section extending axially through the respective wedge112. The axial cross-sections of damper bars 220 have with a perimetershaped for optimizing skin effect by the geometrical layout of thedamper bar and the material selection. The at least one second member120 is intimately radially surrounded by the first member 118. Thoseskilled in the art will readily appreciate that this cross-sectionalshape can be optimized for any given application. This adds a largeamount of Q-axis transient inductance, which improves the transientperformance of synchronous machines in accordance with this disclosureover conventional configurations. The shape can also be optimized totake advantage of the span/cross-sectional area available in the wedges112.

With reference again to FIG. 1, each wedge 112 can have two axiallyopposed end portions 124 of a third material more electricallyconductive than the first member 118 for electrical connection betweenthe second member 120 and the end plates 122. For example, each wedgeincluding the first and second members 118 and 120 can be additivelymanufactured, and layers of copper or other suitable conductor can beadditively manufactured to form the axial end portions 124 of each wedge112. The third material can be the same material as the second materialor a different material from the second material. The wedges 112 caneach be formed with n clearance space between the first and secondmembers 118 and 120 thereof, e.g., by additive manufacturing. Then endplates 122 can be bolted to each end of rotor 102 as indicated by thebolt 126 and bolt holes 128 an 130 in FIG. 1, and the end portions 124will electrically connect the second members 120 in each wedge 122 withthe end plates 122 to form Q-axis damping winding circuits. The plates122 can welded rather than bolted to make the electrical connection inapplications that require less structural capability. It is alsocontemplated that the plates 122 can be a ring that is pressed onto theouter diameter of the wedges 122 making contact via the interference fitto provide the electrical connection with the second member 120 in eachwedge 122.

Conventional high speed systems are utilized for high voltage DC andvariable speed constant frequency systems. These systems requirerectification, and the additional damper circuits as disclosed hereinreduce the commutating resistance, thus making for more efficientsystems than is possible with the conventional configurations.

The methods and systems of the present disclosure, as described aboveand shown in the drawings, provide for Q-axis damping with superiorproperties including full 360° damping coverage with mechanical strengthfor high speed and/or high temperature electrical machines, providingbetter performance for high voltage DC and variable speed constantfrequency systems than traditional configurations. While the apparatusand methods of the subject disclosure have been shown and described withreference to preferred embodiments, those skilled in the art willreadily appreciate that changes and/or modifications may be made theretowithout departing from the scope of the subject disclosure.

What is claimed is:
 1. A wedge for a rotor in an electrical machinecomprising: a wedge including a first member made of a first materialand at least one second member made of a second material, the secondmaterial having a higher electrical conductivity than that of the firstmaterial, the wedge being configured to supply Q-axis damping.
 2. Thewedge as recited in claim 1, wherein the first material has a highermechanical strength than that of the second material.
 3. The wedge asrecited in claim 1, wherein the second material in each wedge forms awedge damper bar extending axially through the respective wedge.
 4. Thewedge as recited in claim 1, wherein the second material in each wedgeforms a plurality of damper bars extending axially through therespective wedge.
 5. The wedge as recited in claim 1, wherein the secondmaterial in each wedge forms at least one damper bar extending axiallythrough the respective wedge, wherein the at least one damper bar has anaxial cross-section with a perimeter shaped for optimizing skin effect.6. The wedge as recited in claim 1, wherein each wedge has two axiallyopposed end portions of a material more electrically conductive than thefirst material for electrical connection between the second material androtor end plates.
 7. The wedge as recited in claim 1, wherein the wedgebody including the first and second material is additively manufactured.8. A method of manufacturing a wedge for rotor of an electrical machinecomprising: additively manufacturing a wedge with a first member made ofa first material and at least one second member made of a secondmaterial, the second material having a higher electrical conductivitythan the first material, the at least one second member forming a Q-axisdamper bar in the wedge.
 9. The method as recited in claim 8, whereinadditively manufacturing includes additively manufacturing layers of amaterial with higher electrical conductivity than that of the firstmaterial on axially opposed end portions of the wedge body forelectrical connection of the damper bar with end plates of a rotor. 10.The method as recited in claim 8, wherein the at least one second memberis intimately radially surrounded by the first member, and the at leastone second member has an arc-shaped cross section.